completion: reduce completable command list

completion: reduce completable command list

The following commands are removed from the complete list:

- annotate             obsolete, discouraged to use
- filter-branch        not often used
- get-tar-commit-id    not often used
- imap-send            not often used
- interpreter-trailers not for interactive use
- name-rev             plumbing, just use git-describe
- p4                   too short and probably not often used (*)
- svn                  same category as p4 (*)
- verify-commit        not often used

(*) to be fair, send-email command which is in the same foreignscminterface
group as svn and p4 does get completion, just because it's used by git
and kernel development. So maybe we should include them.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>